3.5 billion year old organic deposits show signs of life

Sediment in Australian rocks contains the isotopic signature of metabolism.

How long did it take for life to get started on Earth? The planet formed roughly 4.5 billion years ago, although it was uninhabitable for a while afterward. By 2.7 billion years ago, there was unambiguous evidence of complex biological communities in the form of stromatolites, microbial biofilms that can structure sediments in coastal environments. Back in 2006, a paper described evidence that these complex communities have been present as far back as 3.5 billion years ago, based on rocks at the Strelley Pool Formation in Australia.

Now, a new study of rocks from Strelley Pool provides further evidence that these formations were laid down by biological activity. The isotopes of sulfur in the organic material in these rocks show a pattern similar to what we see in material with a known biological origin.

Atomic isotopes are chemically identical (they can undergo the same reactions) but differ in terms of mass. In the fast-paced and energy-sensitive reaction environment inside a cell, that slight difference in mass means that lighter isotopes are more readily incorporated into biological molecules. Over time, even a small difference in the use of lighter isotopes can build up, leading to a significant divergence from the isotope ratio found in non-biological material.

Sulfur has four stable isotopes (out of a total of 25!), with 32S being the most common. Although 33S and 34S are also present in measurable amounts, biological organisms have a strong preference for 32S. For organisms that metabolize organic material by transferring its hydrogen to a sulfur atom (converting sulfate to H2S, the smell of rotten eggs), 32S is greatly preferred. As a result, some of the 34S found in the sulfate in the environment ends up being depleted in the hydrogen sulfide produced by the bacteria.

But there are also some natural processes that produce a bias in isotope ratios, which means that simply getting all the sulfur out of a rock and looking at the overall levels won't tell you much about the source. Instead, the typical hallmark of biological deposits is variability—some layers may simply be trapped environmental materials, while others have a large dose of biological molecules, and should show a skewed isotope ratio. The trick is to look layer-by-layer and search for signs of variability.

That's exactly what the authors of the new paper did, taking thin slices of rock and scanning across them with an ion beam and analyzing the sulfur blasted from the surface. The result was a layer-by-layer measurement of the differences in 34S, with different sampling areas only microns apart.

The isotope ratios ranged widely (from a difference of -17.4 parts-per-thousand to 36.6 ppt). Many of the differences were associated with inclusions of organic material within the rock. Similar values were found in iron-sulfur compounds that had precipitated out. Information from the levels of 33S also suggested the original source of the sulfur was from the atmosphere, consistent with what we know of its likely composition during the Archean era.

As the authors note, this isn't a conclusive demonstration that the layered deposits in these rocks were once biofilms. But it adds to the evidence suggesting they were. And it suggests that, even at this early date, they were using a metabolic pathway that we know is still in use today.

And that evidence suggests that complex biological communities existed as far back as 3.5 billion years ago—which is pretty impressive given that the Late Heavy Bombardment only ended about 3.8 billion years ago. That also stretches out the gap between the obvious presence of life and the origin of multicellular animals, suggesting it might have taken nearly 2 billion years for organisms on Earth to make that leap.

This has me thinking about several 'what-if's' with regards to abiogenesis. Basically the idea of abiogenesis occurring more than once and having a total extinction level event in between (ie life started more than once). This also has me thinking for how long of time period that the initial conditions for abiogenesis were possible.

And from the last paragraph, I'm assuming that there's no appreciable delay between the end of the Late Heavy Bombardment and the first signs of life?

In terms of geological time, that's what this sounds like. Which is really a powerful thing; basically, nearly as soon as the surface of the Earth was something other than molten rock, we had life. Given the right conditions, it appears that living things arise quickly and easily.

If this research is true I would expect life to exist damn near everywhere liquid water and simple organic compounds exist. Life is an emergent property of carbon and water. It's simply not probable life would arise almost as soon as the planet cooled if it were the result of a one in a trillion trillion chance accident.

Perfecting the cell may have taken a while and some happy accidents along the way (symbiotic relationship with mitochondria in our particular instance for example). But self replicating organisms seemingly popped up overnight!

I still wonder why we've only found one form of life on the planet (all life share common DNA sequences). If it is so easy to start up, why doesn't all sorts of different life start up all the time? My pet hypothesis is they do but organisms that use resources most efficiently always win. One reason I'm a little afraid of man-made life, I fear another grey goo existential threat.

And from the last paragraph, I'm assuming that there's no appreciable delay between the end of the Late Heavy Bombardment and the first signs of life?

In terms of geological time, that's what this sounds like. Which is really a powerful thing; basically, nearly as soon as the surface of the Earth was something other than molten rock, we had life. Given the right conditions, it appears that living things arise quickly and easily.

Sample size notwithstanding (i.e. n=1), this certainly seems to be the case for prokaryotes. Remember that it took a further billion years for eukaryotic cells to evolve, though.

If this research is true I would expect life to exist damn near everywhere liquid water and simple organic compounds exist. Life is an emergent property of carbon and water. It's simply not probable life would arise almost as soon as the planet cooled if it were the result of a one in a trillion trillion chance accident.

Perfecting the cell may have taken a while and some happy accidents along the way (symbiotic relationship with mitochondria in our particular instance for example). But self replicating organisms seemingly popped up overnight!

I still wonder why we've only found one form of life on the planet (all life share common DNA sequences). If it is so easy to start up, why doesn't all sorts of different life start up all the time? My pet hypothesis is they do but organisms that use resources most efficiently always win. One reason I'm a little afraid of man-made life, I fear another grey goo existential threat.

Pretty cool science, I just love geology.

Perhaps overnight on Earth's timescales. However, would you consider millions of years to be too short of a timeframe for life to appear?

And from the last paragraph, I'm assuming that there's no appreciable delay between the end of the Late Heavy Bombardment and the first signs of life?

In terms of geological time, that's what this sounds like. Which is really a powerful thing; basically, nearly as soon as the surface of the Earth was something other than molten rock, we had life. Given the right conditions, it appears that living things arise quickly and easily.

Well, there are rather vast uncertainties in all of that. I mean this 'blink of an eye' could be 100 million years, which in evolutionary and chemical terms is a rather vast stretch of time.

Put all this in context, the geological record for the Archean and early Proterozoic are extremely fragmentary. We aren't even sure exactly what geological processes were happening at that time or how similar they were to modern processes. We don't even have conclusive evidence there WAS a late heavy bombardment, it is merely inferred from the very few rock samples we have from the Lunar surface. We certainly haven't well-characterized its duration or extent. When you go back this deep in Earth's history things get very sketchy and confusing, and there's a lot of seemingly contradictory evidence floating around. Truthfully we may never really know with any certainty exactly when or under what conditions life arose on Earth (or even arrived as the case may be).

And that evidence suggests that complex biological communities existed as far back as 3.5 billion years ago—which is pretty impressive given that the Late Heavy Bombardment only ended about 3.5 billion years ago. That also stretches out the gap between the obvious presence of life and the origin of multicellular animals, suggesting it might have taken nearly 2 billion years for organisms on Earth to make that leap.

Clearly we should expect our extraterrestrial overlords to be unicellular monstrosities. The '96 PC game Ascendancy even predicts it of a sort: the "Mebes".

If this research is true I would expect life to exist damn near everywhere liquid water and simple organic compounds exist. Life is an emergent property of carbon and water. It's simply not probable life would arise almost as soon as the planet cooled if it were the result of a one in a trillion trillion chance accident.

There's really no way to know if this is true or not until we start probing planets and moons that have liquid water to prove it one way or the other.

The fact that we are here and able to detect how life on our planet began does not imply that the same is true everywhere else, in and of itself, although the odds seem good.

I still wonder why we've only found one form of life on the planet (all life share common DNA sequences). If it is so easy to start up, why doesn't all sorts of different life start up all the time?

Well, there's speculation that there may be a "shadow biosphere" of non-DNA-based life on Earth. We just haven't found it. I don't always agree with Paul Davies, but he did write a pretty good article on that.

it appears you may be expecting too much too soon. the search is for sulfur based microbes and the search is not limited to Terran but also astrobio. the reason this is significant is, as in Mars and other far reaching projects. the search for what creates life not necessarily creating a definition as yet.

From the third paragraph: ... lighter isotopes are more readily incorporated into biological molecules.

While this is certainly the most common kinetic isotope effect, the reverse is also possible. Inverse kinetic isotope effects are well known in both organic and biochemical reactions. Stabilization at the transition state (halfway between reactant and product) is what drives the KIE, not just isotope size. Not a big error, but I'm amazed that I can finally post a comment on something I know.

I still wonder why we've only found one form of life on the planet (all life share common DNA sequences). If it is so easy to start up, why doesn't all sorts of different life start up all the time?

Well, there's speculation that there may be a "shadow biosphere" of non-DNA-based life on Earth. We just haven't found it. I don't always agree with Paul Davies, but he did write a pretty good article on that.

I still wonder why we've only found one form of life on the planet (all life share common DNA sequences). If it is so easy to start up, why doesn't all sorts of different life start up all the time?

Well, there's speculation that there may be a "shadow biosphere" of non-DNA-based life on Earth. We just haven't found it. I don't always agree with Paul Davies, but he did write a pretty good article on that.

From the third paragraph: ... lighter isotopes are more readily incorporated into biological molecules.

While this is certainly the most common kinetic isotope effect, the reverse is also possible. Inverse kinetic isotope effects are well known in both organic and biochemical reactions. Stabilization at the transition state (halfway between reactant and product) is what drives the KIE, not just isotope size. Not a big error, but I'm amazed that I can finally post a comment on something I know.

Assuming this is evidence of life, 3.5 billion years would be an upper limit not a lower one. It is unlikely the very first organisms would have left a fossil we subsequently found. It is more probably they existed long before this particular fossil was laid down. So perhaps the 100 million year period between water coming to the planet and life developing was more like 50 or 25 million years? Pure conjecture on my part but it seems reasonable. And yes, I consider that a blink of an eye in Deep Time.

I know I'm being overly enthusiastic, I guess I just want to believe in a universe full of life lol.

Thank you for the article link MJ. I think it was that SA article that got me thinking about how often life would arise in the first place, but I'd forgotten much of what it had to say.

My thinking is that Jupiter would be the most likely place is the solar system to have current life. There is mucho differential energy available in different layers that are mixing all the time allowing semi stable systems to come into being allowing life to organize and become stable.

I still wonder why we've only found one form of life on the planet (all life share common DNA sequences). If it is so easy to start up, why doesn't all sorts of different life start up all the time?

Well, there's speculation that there may be a "shadow biosphere" of non-DNA-based life on Earth. We just haven't found it. I don't always agree with Paul Davies, but he did write a pretty good article on that.

I find the "first to the party eats all the food" hypothesis compelling, and the author doesn't address that. Let's say that abiogenesis is relatively easy, but doesn't happen multiple times in a million years. That's consistent with life emerging almost immediately on Earth and any other habitable planet; a delay of a few million years is negligible.

It's easy to imagine one, single organism capable of successful reproduction forming in this way, then in the span of a few million years spreading around the globe and consuming most available resources. Any later abiogenesis is extremely difficult because most important molecules are now already locked up, and a strain of life with a tens of millions of years head start is definitely going to outcompete any primitive newcomer that miraculously manages to form.

The bacteria vs. archaea argument (different lineages, but neither has wiped out the other in billions of years) doesn't apply, since these branches formed simultaneously, and therefore started from equal positions, by virtue of having a common ancestor.

Exactly!! Unbelievers most foul! ...actually, I think YOU are an apostate too. It was actually Sunday, October 23, 4004 BC

...at noon.

Eastern Standard Time (sniff)

Repent!!!

No, no, no. The Earth had to be created in the late afternoon. Because as soon as he was done separating day from night, there was evening and there was morning, the first day. And we know it wouldn't have taken any time to create the Earth and separate day from night. It's God. He can do that instantly. So he must have done it right before evening started.

Now, the really sweet trick was creating day (and even plants) before creating the Sun. But, again, it's God. If anyone can do it, he can.

I thought if you worked the calandar backwards, October 23, 4004 BC turns out to be a Thursday.

It could have something to do with this.

Wikipedia - Pope Gregory XIII wrote:

This was verified by the observations of Clavius, and the new calendar was instituted when Gregory decreed, by the papal bull Inter gravissimas of 24 February 1582, that the day after Thursday, 4 October 1582 would be not Friday, 5 October, but Friday, 15 October 1582.

Wow, it took 22 comments before someone tried to turn this article into a religion-bashing nerd-fest without the slightest provocation this time. Congratulations, you may be evolving.

Hmm, methinks thou doth protest too much. How do you get "religion-bashing" out of people laughing at the fact that there are still young earth creationists around, as we watch the zillionth piece of evidence for evolution and deep time added to the already sky-high pile?

Every one of those mocking comments mocks a demonstrably false belief, *not* a whole religion. And disproving demonstrably false beliefs is the domain of science, *not* religion. When a religion or anyone else start making testable statements like "the earth is 4000 years old", they have entered the domain of science, and *deserve* to be mocked if they don't respond to reason.

BTW, there's a good chance that rising sea levels will cause the extinction of the remaining stromatolites.

They live in extra-salty water which would kill off most of the normal sea life and keeps the stromatolites safe from predators. Once salt levels in their environment are equalized with the normal ocean, then they're ripe for the taking.

Nice! I liked the 3.5 Ga bp (billion years before present) stromatolite work, they looked at microscale too to test for microbial presence, so it is good to have another test. The oldest unambiguous find of life is ~ 3.2 Ga bp (in both Australia and Africa), so these combined results should push life back another 300 Ma.

It would be interesting to see similar work for the Nuvvuagittuq greenstone belt, since it can date all the way back to ~ 4.28 Ga bp and there has been web sites citing unpublished sulfur cycle results.

In that context one should note that the Late Heavy Bombardment is no longer a solid constraint for abiogenesis. Model work shows it is survivable even for mesophiles, who can repopulate faster than any realistic impact rate sterilizes. [ http://www.nature.com/nature/journal/v4 ... 08015.html ] There is follow up work on a Goldilock crustal survival zone ~ 1 km down, which allows for survival even in the presence of crust busters. Life is a plague on a planet.

Quote:

That also stretches out the gap between the obvious presence of life and the origin of multicellular animals, suggesting it might have taken nearly 2 billion years for organisms on Earth to make that leap.

That is suggested by whole genome results too.

By way of protein fold families, a clock proxy tell us the the RNA/protein world was ~ 20 % of the clock and the DNA LUCA another ~ 20 %. The subsequent domain diversification is then occupying only about half the biosphere lifetime. ["The evolution and functional repertoire of translation proteins following the origin of life", Goldman et al, Biol. Dir. 2010.]

The essential features of this uncalibrated clock proxy, including gene birth, duplication, transfer and death rates, was tested by a self-calibrated gene family model, and show that diversification likely happened correlated with atmosphere oxygenation ~ 2.5 Ga bp. ["Rapid evolutionary innovation during an Archaean genetic expansion", David et al, Nature 2010.]

When it comes to complex multicellular life, it is present only in eukaryotes. Lane's energy theory for eukaryotes predicts why that is so, a ~ 10^5 larger energy density because of mitochondrial endosymbionts for protein turnover means larger genomes, and why it had to happen after atmosphere oxygenation.

I don't understand this article. I think that the effect is a primary kinetic isotope effect. IIRC, a primary kinetic isotope effect is limited to (ratio of atomic weights of isotopes)^.5. For the sulfur isotopes, this is a small number. The paper says, "The isotopic fractionation associated with assimilatory sulfate reduction is generally small (i.e., approximately 1–3‰) (37); thus, biosulfur has an isotopic composition close to that of ambient sulfate." I don't understand what they say to get from here to the significant changes the Ars account gives. Can anyone explain?

dh87, it is probably a typo. Bontognali is not spelled correctly either.

Kevin G wrote:

This has me thinking about several 'what-if's' with regards to abiogenesis. Basically the idea of abiogenesis occurring more than once and having a total extinction level event in between (ie life started more than once). This also has me thinking for how long of time period that the initial conditions for abiogenesis were possible.

bagok wrote:

I still wonder why we've only found one form of life on the planet (all life share common DNA sequences). If it is so easy to start up, why doesn't all sorts of different life start up all the time? My pet hypothesis is they do but organisms that use resources most efficiently always win.

Essentially between having an ocean with hydrothermal vents from crustal rework (going into plate tectonics) that can supply local redox energy until you have independent cells. Already Darwin suggested that the reason why we don't see renewed abiogenesis attempts is because current life consume the raw material.

There is for example no reason why a late Moon, which is now possible since earlier constraints have been lifted, sterilized Earth and abiogenesis had to restart.

nickf wrote:

Sample size notwithstanding (i.e. n=1), this certainly seems to be the case for prokaryotes.

When you test a stochastic process model, say a simplest possible Poisson model of repeated attempts, you can get away with estimates of parameters instead of estimates of events.

Hence the early date _is_ informative, and a < 1 Ga period before life translates to a deterministically easy process @ 3 sigma. This is IMO why these results are so important, as you get to ~ 3.2 Ga bp you start to lose that testability. (Because the underlying exponential distribution stacks its probability mass so early.)

So perhaps the 100 million year period between water coming to the planet and life developing was more like 50 or 25 million years?

Essentially possible, but the timing isn't easy to tell. I'm not giving refs here, because its late:

Initial water content of Earth-Moon and Mars is now known to have been the same, and it is also what an updated model of the protoplanetary disk predicts for the inner terrestrials. It is fully consistent with today's Earth water.

So later water delivery is neither necessary nor likely. Ocean formation then happened after crust formation and volcanic delivery of the mantle hydrogen.

Assume that the hydrothermal vent theory is correct. It is likely, because it supplies organics, redox energy and subducting plate vents should contribute the necessary polyphosphates too.

Then free protocells should originate in the maximum lifetime of these vents or < 0.1 Ma. This has been modeled as entirely possible. Or possibly you had migrating protometabolic systems by way of migrating organic or semiorganic catalysts, in the same way you today have migrating life between vents. In any case, the massive parallelism gives a short time between chemical and biological evolution.

But as I commented already, the sterilizing Earth-Moon impact date has become relaxed. New models for core formation can predict observed isotope constraints while pushing the massive impact which contributes the last 10 % of Earth mass. The dates coincides with possibilities open up by redating of Apollo samples.

Coincidentally, if you take the Archaean Expansion model and use its earliest gene birth rates in a toy model on a reasonable RNA/protein cell descendant, you get that the first genes originated ~ 4.31 Ga bp.

This would leave ~ 40-50 Ma between a worst case late impactor and the RNA world, which is plenty of time for hydrothermal vent models.

Sample size notwithstanding (i.e. n=1), this certainly seems to be the case for prokaryotes.

When you test a stochastic process model, say a simplest possible Poisson model of repeated attempts, you can get away with estimates of parameters instead of estimates of events.

Hence the early date _is_ informative, and a < 1 Ga period before life translates to a deterministically easy process @ 3 sigma. This is IMO why these results are so important, as you get to ~ 3.2 Ga bp you start to lose that testability. (Because the underlying exponential distribution stacks its probability mass so early.)

That wasn't quite the point I was making though, i.e. as far as we know it took around a billion years for eukaryotes to evolve from prokaryotes. Presumably the advent of oxygenic photosynthesis greatly facilitated this process. The protist -> metazoan jump seems quite easy in comparison.

Wow, it took 22 comments before someone tried to turn this article into a religion-bashing nerd-fest without the slightest provocation this time. Congratulations, you may be evolving.

Hmm, methinks thou doth protest too much. How do you get "religion-bashing" out of people laughing at the fact that there are still young earth creationists around, as we watch the zillionth piece of evidence for evolution and deep time added to the already sky-high pile?

Every one of those mocking comments mocks a demonstrably false belief, *not* a whole religion. And disproving demonstrably false beliefs is the domain of science, *not* religion. When a religion or anyone else start making testable statements like "the earth is 4000 years old", they have entered the domain of science, and *deserve* to be mocked if they don't respond to reason.

There are none of those people here, none of the stragglers that chance around every once in a while made any comments to this article. Everybody around knows what evolution is, how it works and have no trouble with the concept. Those comments just amount to a kind of circle-jerk: "look at us, how clever we are. We have achieved the ultimate knowledge about the universe yet there are these unwashed masses who do not understand even the basic concepts about time, space and life. Let us all laugh at them. Meanwhile we'll be such jerks about it, they won't want to listen to us, even if there may be a few among them who may not be as close-minded as the others and might benefit from some explanations but fuck them as well. Let us alienate them too."

They look like the bullies who make fun of the slow kids at school. Some find it funny. I find it sad for all the parties concerned.

That wasn't quite the point I was making though, i.e. as far as we know it took around a billion years for eukaryotes to evolve from prokaryotes. Presumably the advent of oxygenic photosynthesis greatly facilitated this process. The protist -> metazoan jump seems quite easy in comparison.

You are polite, it wasn't at all the point you were making. I just jumped on to the often claimed point of low sample size, because it is relevant to the context of this.